Studies will be continued on a newly observed property of snake venoms: the enzymatic inactivation of human plasma proteinase inhibitors (PPI). Research in progress indicates that venom proteinases inactivate antithrombin II via limited proteolysis. Alpha 1 antichymotrypsin is also enzymatically inactivated. Inter-alpha-inhibitor and Cl inhibitor will be reacted with venoms, and proteinase(s) causing their inactivation will be purified. Digestion products will be isolated and characterized to determine the cleavage sites on each inhibitor. This research, coupled with previous observations on venom inactivation of alpha l proteinase inhibitor, will test the hypothesis that venom proteinases inactivate PPI by limited proteolysis of a susceptible bond at or near the inhibitor reactive site. Preliminary observations on the release of an active venom proteinase from its complex with alpha 2 macroglobulin (alpha 2 M) in the presence of other partially purified venom proteinases will be extended. The high molecular weight venom proteinase(s) causing the release will be purified, and their effect on the alpha 2 M complex studied to determine the mechanism of action of this unusual type of alpha 2 M-proteinase interaction. The in vivo effects of an active fluorescent-labeled venom proteinase and uptake of the alpha 2 M-venom proteinase complex by cultured cells will also be studied. The objective of these investigations is to further knowledge of the mechanism of interaction between PPI and proteolytic enzymes. A better understanding of the role of proteolysis in snakebite pathogenesis and venom toxicology should result. The inactivating proteinases could prove useful in studying the role of PPI in the control of physiological processes. The proteinases may also be applicable to animal model systems to study diseases, e.g., emphysema, involving specific PPI deficiencies.